Voltage dropping at WOT pulls. Need Help!

[04Mach1Blurr]

So I am in the middle of having my car tuned. Tuner sees that the voltage is dropping from 13.5 to 12.1 under WOT at 4500rpm. Battery is a new Motorcraft, Alternator is a PA 160 with a 3.5 inch pulley. From the battery at idle and normal driving its at 13-13.5 volts. But as soon as its under boost it starts dropping. I swapped to a brand new OEM alternator and used the 3.5 inch pulley, same thing, 13 down to 12 volts under WOT. Tried using the stock smaller pulley on the OEM alternator and it dropped even quicker at idle and at WOT to high 11s.

I'm at a loss of knowledge and need some help.

Run-down of the car:
04 Mach 1
04 Terminator Longblock
08 GT500 Posi Blower
60lb injectors
Ford GT fuel pumps (2)
Wiring upgrade to FPDM
Modified FPDM.

Thank you

 

[04Mach1Blurr]

Just data logged a little bit sitting in the drive way. Wanted to check the FPDM and see if there was a difference between the modified one and the oem one. No difference really noticeable. The FPDC was at .40 at idle and under quick WOT it maxed at .49.

 

[slow5oh]

I'm having this same issue currently, so I will be watching, and let you know if I figure out what's causing my problem.

 

[04Mach1Blurr]

I'm having this same issue currently, so I will be watching, and let you know if I figure out what's causing my problem.

Do you have an ongoing thread? I'd like to see what you've tried as well.

 

[whi tri]

Buy any chance did you get your rebuilt alt from sterling ford? I have a thread right now for a possible shitty new alt

 

[04Mach1Blurr]

Buy any chance did you get your rebuilt alt from sterling ford? I have a thread right now for a possible shitty new alt

I got mine from Chantilly's Ted Britt

 

[racebronco2]

I can tell you this has been a problem for a while on the Cobra's. I had the same problem a while ago when i was having alternator problems. My tuner checked the voltage at the battery which was 1/2 higher than it was at the ecu.

I think a solution would be is to do a wire upgrade similar to the bap wire upgrade so the the ecu gets the thru voltage without having the voltage drop associated with the thinner wire.

 

[highcompression]

This is why I like a BAP, it will hold voltage in instances like this .... Or at least "lessen" the effects.

.... I've been running the Aluminator 135a alternator now for two years, NO issues. Just picked up another @ Summit Racings annual "scratch and dent" sale. Found a demo with a dig in the pulley and got it for 70 bucks ! Talk about lucky and a good spare ! I believe part number is FMS- 1300-46sc (or something close to it). BEST alternator I've ran ....... And I've ran "everyone's"

 

[highcompression]

And yes, I also did the 8awg wiring upgrade also.

 

[fbody83]

I would say it's the alternator but it's strange that the new OEM unit does the same thing. Maybe get the OEM unit load tested to make sure there isn't a defect with it first and then you can eliminate the alt as the culprit.

 

[svt4me38]

I'm currently suffering the same issue, fixing my fuel rails first, then I'm alternator hunting!

 

[whi tri]

I'm actually in the same boat also. I asked where you got it from because I got 2 from sterling ford. The first one had a bent shaft and the second one which is on my car at wot sees 12.6 ish. With a new battery. I'm going to add a new ground from alt to chassis and a new power cable from alt to fuse block and see what happens.

 

[04Mach1Blurr]

I'm actually in the same boat also. I asked where you got it from because I got 2 from sterling ford. The first one had a bent shaft and the second one which is on my car at wot sees 12.6 ish. With a new battery. I'm going to add a new ground from alt to chassis and a new power cable from alt to fuse block and see what happens.

Please let me know what you find on that work.

 

[04Mach1Blurr]

I can tell you this has been a problem for a while on the Cobra's. I had the same problem a while ago when i was having alternator problems. My tuner checked the voltage at the battery which was 1/2 higher than it was at the ecu.

I think a solution would be is to do a wire upgrade similar to the bap wire upgrade so the the ecu gets the thru voltage without having the voltage drop associated with the thinner wire.

What other wires need to be upgraded? I have 1 gauge power wire from the battery to my block i used on the drivers side of the engine bay to the oem wiring there, as well as upgraded FPDM wiring

 

[calypso92coupe]

So! Is there a wiring upgrade for the ecu supply? Link?

 

[03Cobrra]

I'm having the exact same problem literally word for word. Tried 3 alternators, 2 batteries, checked all the grounds fuses etc, not sure what to do at this point. When your voltage drops into the 11's does the car still run normally or are you having other issues because of it? When I datalog and the voltage drops my laptop loses connection with the car and the log goes blank.

 

[Mystic03]

are you guys still on the returnless system?

 

[04Mach1Blurr]

I'm having the exact same problem literally word for word. Tried 3 alternators, 2 batteries, checked all the grounds fuses etc, not sure what to do at this point. When your voltage drops into the 11's does the car still run normally or are you having other issues because of it? When I datalog and the voltage drops my laptop loses connection with the car and the log goes blank.

Yea same issues. When I went to datalog today it dropped as low as 12.2, hasn't gotten into the 11s yet. But i did notice that my dash gauges were shutting on and off 3 times and then went back to normal. This was about 1 full min after doing a pull and coming to a stop after exiting the highway. and it stopped my SCT X3's data logging.

are you guys still on the returnless system?

Yes, 60lb injectors, cobra fuel hat with pprv delete, wiring upgrade, (2) Ford GT pumps, modified FPDM

 

[whi tri]

I'm also still return less with a wire upgrade with relay and bap.

 

[03Cobrra]

Yea same issues. When I went to datalog today it dropped as low as 12.2, hasn't gotten into the 11s yet. But i did notice that my dash gauges were shutting on and off 3 times and then went back to normal. This was about 1 full min after doing a pull and coming to a stop after exiting the highway. and it stopped my SCT X3's data logging.




Yes, 60lb injectors, cobra fuel hat with pprv delete, wiring upgrade, (2) Ford GT pumps, modified FPDM

Yea my gauges don't do that but like I said the datalog gets all crazy and nothing is accurate. If you find anything out let me know please. I'm done, I'm beyond frustrated with this stupid problem, I washed the car and put the cover on it and I don't want to see it until someone figures out how to fix this issue.